POS0016 SERUM AMYLOID A CONNECTS LIVER AND JOINT TO PROMOTE MACROPHAGE ACTIVATION AND CHRONIC ARTHRITIS VIA NFAT5
Authors: M. LI, Y. M. Kim, H. M. Kwon, J. H. Park, J. Jin, D. Kim, W. U. Kim
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> The nuclear factor of activated T-cells 5 (NFAT5) is a member of the Rel family of transcription factors that can be activated by hypertonic stimuli <sup>[1]</sup>. It remains unclear, however, whether NFAT5 is required for damage-associated molecular patterns (DAMPs)-triggered inflammation and immunity. Serum amyloid a(SAA) is an endogenous toll-like receptor (TLR) ligand functioning as a DAMP responds to bacterial endotoxins <sup>[2]</sup>. In response to infection and inflammation, innate immune cells secrete pro-inflammatory cytokines, in particular IL-1β and TNF-α, to which the liver responds by producing acute-phase reactants <sup>[3]</sup>. Further identification of such pathologic process by acute-phase reactants will allow for better selection of therapeutic targets as well as a greater understanding of the mechanisms underlying chronic inflammation. <h3>Objectives</h3> To investigate SAA, an acute phase reactant as well as a TLR ligand, activates NFAT5 in macrophages of arthritic joints after being secreted from the liver and thereby promotes chronic inflammation. <h3>Methods</h3> SAA-induced upregulation of NFAT5 expression and activity in RAW264.7 cells, mice bone marrow derived macrophages and human peripheral CD14+ monocytes were assessed by western blot and/or luciferase reporter assays. SAA-accelerated arthritis in mice was generated by injecting SAA (5 μg ×1) in the affected joint of mice with a suboptimal form of IL-1β-induced arthritis, which was induced by injection of methylated bovine serum albumin (mBSA, 200 μg ×1) and/or IL-1β (250 ng ×2). Decrease in arthritis severity and inflammatory cell infiltration by <i>Nfat5</i>- and <i>Tlr2</i>/4-deficient mice, specific knockout of myeloid <i>Nfat5</i>. We used adenoviral vector system and overexpressed SAA gene in the liver exacerbates chronic arthritis in mice. <h3>Results</h3> Like hypertonic stimuli, several damage-associated molecular patterns (DAMPs), including SAA, MRP8, and HMGB1, can induce expression of NFAT5, an osmo-sensitive transcription factor. In particular, acute phase reactant SAA substantially increased NFAT5 expression and activity in RAW 264.7 and primary macrophages. SAA-mediated NFAT5 upregulation was operative via TLR2/4-JNK signaling pathway in macrophages. In addition, triggering of the 'SAA-TLR2/4-NFAT5' axis provoked migration and chemotaxis of macrophages and aggravated chronic arthritis in a CCL2-dependent manner. Intra-articular injection of SAA markedly accelerated macrophage infiltration and arthritis progression in mice. By contrast, genetic ablation of NFAT5 or TLR2/4 rescued the pathology induced by SAA, confirming the SAA-TLR2/4-NFAT5 axis in <i>vivo</i>. Myeloid-specific depletion of NFAT5 also attenuated SAA-accelerated arthritis. Notably, chronic arthritis in mice strikingly induced SAA overexpression in the liver. Conversely, forced overexpression of the SAA gene in the liver accelerated joint damage, indicating that the liver contributes to bolstering chronic inflammation at remote sites by secreting SAA. <h3>Conclusion</h3> In summary, this study underscores the importance of the SAA-TLR2/4-NFAT5 axis in innate immunity, suggesting that acute phase reactant SAA mediates mutual interactions between the liver and joints and ultimately aggravates chronic arthritis by enhancing macrophage activation. <h3>References</h3> [1]Lopez-Rodríguez C, et al. NFAT5, a constitutively nuclear NFAT protein that does not cooperate with Fos and Jun. <i>Proc Natl Acad Sci U S A.</i> 1999;96(13):7214-7219. [2]Gong T, et al. DAMP-sensing receptors in sterile inflammation and inflammatory diseases. <i>Nat Rev Immunol.</i> 2020;20(2):95-112. [3]Nefla M, et al. The danger from within: alarmins in arthritis. <i>Nat Rev Rheumatol.</i> 2016;12(11):669-683. <h3>Acknowledgements</h3> This study was supported by a grant from the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT (2015R1A3A2032927 to W.U.K.) and a grant from NRF by the Ministry of Education (2017R1D1A1B04033009 to D.K. and 2020R1I1A2069425 to Y.M.K.) <h3>Disclosure of Interests</h3> None Declared.